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Drum or Fluid Bed
oldgrumpus
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Posted on 12/01/2023 5:36 PM
I'm sure this has already been discussed too much already, so I apologize in-advance...

Drum roaster versus Fluid Bed pros & cons. Is there such a comparison that is out there somewhere? Not looking for a full discussion, just hopefully a side-by-side list? Concise.

If it doesn't maybe I can start one. You may ask why I would do this since I already have a pretty good drum roaster. Well, I do love my roaster, but one characteristic with a high-mass drum is heat input changes take time to take effect. It's not really a problem now that I've become familiar with this and can plan heat changes in advance, but impulsive changes to make corrections when things don't go as expected don't usually help too much.

So, I'm thinking about a hybrid with a thin, low-mass drum with no burner under the drum but somewhere off to the side and heat brought in through the back much like some of the big boy roasters in the commercial world.

Thoughts?
Clever Coffee Dripper
Grinder: Macap M4
Roaster: Completed drum roaster project photos shown here:
Photos https://goo.gl/ph...Da6K4wfqw5
Videos https://www.youtu...Bd1NrdpSUH
Build thread https://homeroast...post_38189
 
krampe
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Posted on 12/02/2023 8:40 AM
with equivalent batch sizes the total roast time is better since fluid beds are a little faster and take way less time to warm up.
now I don't have a true fluid bed roaster but I enjoy being in and out in 20minutes including all setup and tear down
 
allenb
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Posted on 12/03/2023 12:46 PM
I'm not aware of any side by side comparisons although they probably exist out there. Not sure how useful they would be since there are so many variations of the fluidbed.

Here's some thoughts I can share from my experience with both roasters.

By nature, conventional drum roasters can easily maintain a basic bean temperature profile pattern with very little input control changes needed. The downside is, by nature, the thermal mass that allows the above benefit also prevents it from being "quick on it's feet". Sort of like comparing a large sailing vessel with a jet ski.
A shortcoming of the conventional drum roaster is it's lack of ability to do ultra short (6-8 min) without potential damage to the beans exterior cell structure. For some of the Nordic profiles, the faster profile is a necessity. Some do not see this as much of a shortcoming since green offerings that allow ultra short, ultra light roasting are a small % of available coffees sold.

By nature, fluidbed roasters can do ultra fast roasts as long as roast chamber and blower design are optimized for proper bean flow allowing high RoR without damage to bean structure.
By nature, when manually controlled, fluidbed roasters require much more attention to maintaining proper heat input levels to follow a desired profile curve.

As I continue to experiment with fluidbeds and other types capable of a fast roast without potential damage to the bean, I'm finding I can coax much more nuance in varietal detail than is possible with my 1 lb gas fired drum. I get really good results from the drum roaster but I'm always missing some of the fine details some of the higher end green coffees have to offer.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
oldgrumpus
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Posted on 12/03/2023 1:42 PM

Quote

I'm finding I can coax much more nuance in varietal detail than is possible with my 1 lb gas fired drum. I get really good results from the drum roaster but I'm always missing some of the fine details some of the higher end green coffees have to offer.


allenb, I think this quote from your post above is what I'd like to explore some. Can you elaborate and make some comparisons to your best efforts in the drum roaster vs. how you get "more" from the FB roaster? Not sure if it can be shown with graphs or just verbally explaining times and temps?
 
allenb
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Posted on 12/03/2023 5:45 PM

Quote

allenb, I think this quote from your post above is what I'd like to explore some. Can you elaborate and make some comparisons to your best efforts in the drum roaster vs. how you get "more" from the FB roaster? Not sure if it can be shown with graphs or just verbally explaining times and temps?


I'll give it a shot by discussing some examples.

I had been roasting a couple of Kenyas, Burundis and Ethiopian coffees solely on my modified Hearthware Gourmet I bought from snwcmpr which has been extinct for quite a few years. I hadn't attempted roasting any of them in my 1 lb drum since I had only purchased a few lbs of each. Results in the Hearthware were exceptional with lots of floral/spice high notes at a fairly light roast. The roast profile for most of them was nothing fancy and was really just a 2 stage heat profile, around 400F for three minutes which got the beans to yellow at 3 min and 500F for the remainder which had them hitting first crack at around 5:30 and finishing anywhere from 7 to 7:15 at a very light roast. Later, I saw that I had enough of one of the Kenyas to do a 1 lb drum roast so I gave it a whirl using my go-to drum profile which was preheat internal drum area to 375F, highest RoR around 40F/m declining down to 20/m by the time BT hits 340. Beans were at yellow by minute 6:30, first crack around minute 12. Development was around 2 min with RoR averaging between 7 and 10/m.
The coffee was very good and probably as good as I'd ever done in the drum roaster but there was a difference. Grind aroma, while very nice, was missing some floral and spice fragrance I was routinely getting with the Hearthware roasts. Cup quality was very good but was also missing the high notes entirely. I'm not implying that there would not have been a way to screw around with multiple profile tweaks and finally achieve what I was after but I had no interest in going through the trouble since it was so simple in the Hearthware.
With some coffees, there's not a lot of difference between my drum and fluidbed and a small percentage of them don't like the shorter 6 to 7 minute profile and need at least a 9 min profile otherwise end up with some underdeveloped green/woody off notes.
So, my take is this, with a fluidbed, you at least have the option of trying a new coffee using a shorter profile to see what it's capable of in the high note sparkle realm but with my drum, it has to be an extremely exceptional coffee to ever produce that magic.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
oldgrumpus
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Posted on 12/04/2023 1:06 PM
Thanks for that fantastic explanation! I totally get it. Although I'm probably never going to build another roaster, I do think that I can play with some shorter roasts. To get the shortest roast possible, I'd think that a pre-heat temperature should not exceed the target drop temp. I can raise it a bit. Also, my 3lb roaster has 31,300 which gives me more than I've been using. My roasts have been FC @ about 9 minutes and drop at about 12 minutes. I suspect I can shorten all by about 2 minutes or so, maybe a bit more. I'll try it on the next roast.

Again, your post answered a lot of my nagging questions. Thanks!
 
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